1. Field of the Invention
The present invention relates to a shaftless butterfly valve apparatus of the type mounted along a pipe which carries fluids, slurries, gases, or other flowing materials and substances.
2. Description of the Prior Art
A conventional butterfly valve typically includes a circular disc member which is pivotally mounted inside a cylindrical bore defining a flow passage. The disc is mounted to turn on an axis extending transversely of the flow passage between an open position where its plane is generally coincident with the direction of flow and a closed position where its plane is at a right angle to the direction of flow. In a closed position a fluid seal is provided either by the outer periphery of the disc engaging a sealing member provided in the interior of the valve housing or by a sealing member carried on the periphery of the disc engaging a seating surface on the interior of the housing.
Conventional butterfly valves have many disadvantages. One disadvantage is that butterfly valves mounted on pivot shafts, as described above, are relatively expensive to manufacture. One major cost item is the necessity of present state of the art butterfly valves to utilize complex castings or heavy flame cut segments for valve housings due to the need to provide external rotary bearing support for the pivot shaft.
Another disadvantage common to conventional butterfly valves is that they are often difficult to operate because of the binding between the rubber seal and valve seat. This often prevents proper seating of the valve, resulting in undue leakage between the valve and seat. Moreover, the rubber seal often deteriorates over time due to excess binding, particularly at high temperatures.
Furthermore, the typical prior art valve has an actuator which would typically be a gear box or scotch-yoke mechanism with a lever or crank attached. This arrangement increases the size of those portions of the valve mechanism positioned externally of the pipe or valve housing and for many applications this is a further disadvantage.